do RPi3 3.3/5V pins output constant voltage even if the RPi power supply is changing voltage?

Question

I want to power my RPi with a lithium ion battery. The RPi will be powering some devices which require constant voltage to power them.

If I use a battery as supply for the RPi (which changes as it depletes), will the 3.3 or 5V pins still output a constant voltage?

I saw this post here: Does the Raspberry Pi 3 regulate the voltage on its 5V pins?

which seems to rule this out for the 5V pin, but I wasn't clear on the 3.3V pin, can anyone advise?

This post: https://raspberrypise.tumblr.com/post/144555785379/exploring-the-33v-power-rail

appears to confirm the constant 3.3V output, but would appreciate confirmation by someone with more experience

Answer 1

Practically speaking, you cannot power the RPi by a raw Li-Ion cell: its voltage will be in the range of 3..4.2V while the RPi requires 4.75V..5.25V. You will need to boost the Li-Ion cell voltage to 5V.

Answer 2

The Pi has an on-board regulator which supplies the many voltages it requires (including 3.3V) although different models achieve this by diverse means.